Fuel supply system for spill type burners



A g- 6, 1952 F. H. CAREY FUEL SUPPLY SYSTEM FOR SPILL TYPE BURNERS 2 SHEETS-SHEET 1 Filed Jan. 14, 1948 y, QN..

Aug. 26, 1952 F, CAREY I v 2,608,247 FUEL SUPPLY SYSTEM FOR SPILL :TYPE BURNERS Filed Jan. 14, 1948 7 zsmfi'is-safis'r 2 n Patented Aug. 26, 1952 FUEL SUPPLY SYSTEM FOR SPILL TYPE BURNERS Frederick Henry Carey, Cheltenham, England, as-

.ham, England 7 signor to Dowty Equipment Limited, Chelten- Application January 14, 1948, Serial No. 2,343

, In Great Britain January 2t), 1947 6 Claims. (01. 158-3624) The various designs of burner used in continuous combustion gas turbines may be divided into two categories of which one category comprises the more generally used burners known as simple direct-injection burner nozzles in which all the fuel supplied to the burner passes out through its discharge. orifice, and the other category. comprises burners'in which, except during certain operating conditions, only a proportion of the fuel supplied to the burner nozzle passes out through the discharge orifice and the remainder flows back along a return line. This invention is concerned with liquid-fuel supply systems for thoseburner nozzles of the second mentioned category in which fiow through the return orifice precedes any discharge through the discharge orifice, and for convenience all such burners or nozzles are hereinafter referred to as spillburners as herein specified. The patents to Peabody,'No. 1,628,424 and to Bargeboer No. 2,079,430 disclose examples of such burner nozzles, although the supply system of Peabody differs greatly from that herein disclosed and claimed. As at present constructed, these burner nozzles have a discharge orifice arranged as a co-axial outlet from a swirl chamber into which the fuel is supplied tangentially, the return or spill orifice being axially in line with the dischargeorifice but of larger capacity so that until the return .fiowis retarded in some way no discharge from the discharge orifice takes place, the fuel simply swirling in the swirl chamber and passing off by the return line. The output of such burners is dependent, not on the volume of fuel circulated, nor the rate of circulation, nor yet alone or necessarily on the rate of supply of fuel, but rather on the amount by which the fuel supplied exceeds the return flow capacity of the system. I

Spill burners have the inherent advantage over the simple direct-injection burners that they can produce a satisfactorily atomized spray throughout a greater flow range without necessitating unduly high pump pressures. This is an important consideration with gas turbines for aircraft propulsion, owing to the wide altitude range within which the aircraft has to fly which brings about very considerable variations in the engine fuel requirements for the same engine speed. The problem is rendered more acute by the fact that the pumps used for supplying the fuel to the burners are for various considerations more usually driven by the engine, in order to save the weight of separate pump-drive means,

hence pump output varieswith engine speed.

From the point of view of fuel economy the modern tendency is for aircraft to be designed to operate at great altitude at which the engine requires considerably less fuel for the same engine speed than it would require at a low altitude. The reason why spill burners which possess this advantage are not more generally employed is because the nozzles have not hitherto been given a satisfactory environment, the supply systems hitherto associated with these nozzles being unsatisfactory particularly when relatively small quantities of fuel are being discharged from the burners, as is particularly the case at high altitudes. The known systems have been unable to cater in a satisfactory manner for maximum and minimum engine speeds at extreme altitudes.

The primary object of the present invention is to provide an improved system for supplying fuel'to aircraft spill burners as herein specified, which affords a more efiicient atomization of the, discharged fuel and also a greater sensitivity of control. In its application to aircraft propulsion, the invention affords better atomization having in mind the considerable variations in engine fuel requirements at extreme altitudes of flight, and bearing in mind that the fuel is usually supplied by oneor more pumps driven by the engine.

According to one aspect, the present invention consists in a liquid-fuel supply system for spill burners as herein specified, in which the operation of two pumps are coordinated to the desired ends. One thereof, a circulating pump, operates normally to circulate fuelin a circuit including the swirl chambers of the burner nozzles, said circulating pump being so rated in relation to the circuit that it maintains the circuit substantially at capacity without of itself causing any discharge through the nozzle discharge orifices, and the other a supply pump, operates normally, and under theinfiuence of a manually controllable throttle means, to inject into the circulating flow a controllable fiow of fuel whose presence causes the capacity of the circuit to be exceeded to cause atomized fuel to issue from the nozzle discharge orifices at'a controlled rate. Also, according to the invention, a liquid-fuel supply system for an aircraft continuous combustion turbine engine having spill burners as herein specified, comprises such a circulating pump which may be driven by the engine and is operative normally to circulate fuel around a circuit including the burner nozzles, and such a supply pump which 3 also may be driven by the engine and is operative normally to inject fuel into the circuit under control of throttle means as necessary to maintain a required engine speed or to effect any change thereof.

The supply pump may be of the variable displacement type, or of the fixed displacement type with an associated controllable by-pass. This pump may inject into the circulating flow at some point in the supply line running between the circulating pump and the burner nozzles, but it is preferred so to arrange the system that during normal running of the engine the supply pump injects into the circulating flow at a point in the return line from the nozzles to the circulating pump, wherefore, by reaction along the return line, to impede flow from the swirl chamber by way of the return line, and to effect discharge therefrom, instead, by way of the nozzle discharge orifice.

The invention 'wi-l1 now be described by way 'of'example with reference to the accompanying diagrammatic drawings of which:

Figure 1 shows one system'embodying the invention;

Figure 2 is a fragmentary sectional view of a detail of the nozzle drawn to an enlarged scale, and

Figure 3 shows a modif ed pump unit and coordinate control device for the same.

In the system shown in Figures 1 and 2, fuel is supplied to a group of nozzles I (only one of which is shown). n'll'the nozzles I have their inlets 2 connected with what is known as a burner ring 3, namely, a fluid flow ring whence fuel flows to several nozzles, and their return lines 4 connected'with what is known as a collector ring '5, which is a similar fluid flow ring whereto unused fuel flows from the several nozales. In the particular example shown, each nozzle has a swirl chamber '6 into which the 'fuel is supplied through anumber of tangential passages I so that the incoming fuel swirls around the wall of the chamber 6 to build up what may be defined as a tube of fuel with a centrally disposed air core. At the "outer end of the swirl chamber 6 the nozzle is formed with a discharge orifice 8 and at the other end of the swirl chamber with a spill orifice 9 which is coaxial With the dischargeorifice 3 and of {greater area. The system eoinprises essentially two "pumps'ofwhich one, a circulating pump I'll, operates to circulate 'fuel around a circuit "including a supply line H, the burner ring 3, the swirl chambers 6 of all'theno'zzle's I, the collector ring and a return line I2, wherein is 'a non-return valve l2a. The other'b i p, a suppiy'pump l3, serves to 'withdraw fuel from a tank T4 and to discharge "it through "a metering valve or throttle l5, whereby the supply pumps effective delivery is regulated, and "along a, line T6 to inject the fuel into 'the circulating new set up by the circulating pump T0.

The circulating pump I'D operates as a "fixed delivery'pump and'will usually be engine driven. The supply pump I3 is also usually drivenby'the engine and operates'a's a variable delivery pump to inject 'fuel into the circulating now at a selected rate. In the example under consideration, each pump comprises a ported valve spindle ll around which there rotates a radial cylinder assembly [8 having radiallydisposed reciprocating pistons 19 provided at their outer ends with slipper bearing pads 20 running against the inner surface of a track ring 2| the eccentricity 4 of which with respect to the axis of the valve spindle l'l determines the operative strokes of the pistons. The track ring 2| of the circulating pump I0 is of fixed eccentricity with respect to the corresponding valve spindle ll. The track ring Zia of the supply pump 13 is mounted to rock about a pivot 22 so that its eccentricity with respect to its valve spindle ll may be varied. For this purpose, the track ring has a projecting finger 23 extending intermediately of the length of a pressure loaded plunger 24 which is influenced by a spring 25 to tend to move the track ring to a position of maximum eccentricity. The plunger 24 is also exposed to the pressure in the delivery line from the pump I 3 which pressure acts in the opposite sense to that of the spring 25. By these means the pump l3 automatically takes up a position in accordance with the setting of the metering valve 15 to maintain a constant pressure in the delivery line 26 running from the pump 'to the metering valve.

In my burner the pressure impressed up'on'the fuel by the circulating pump I 0 is employed only for the purpose of conveying the fuel through the supply line H and into the chamber 6. Once it enters the chamber -6 its pressure is largely converted into movement, and because it enters tangentially at orifices Tits movement-is a whirling movement about the axis of thechainber. It its escape from the chamber were impeded, the chamber would fill up, but by "design the return line [2 is of adequate capacity to accommodate all the fuel which the circulating pump it alone can deliver, and this offers no obstacle to free escape. Its first and only obstacle is the spill orifice 9, and it fills up 'only until it overcomes that obstacle, whereupon it flows over the same. Since "there is no other impedance to'its escape, undersuch conditions, there is no further filling up of the chamber '6, for instance, 'to the level of burner discharge orifice 8, and the fuel merely whirls about the chamber in a tube. If it could be assumed that all this time the supply pump i=3 is running, but is in neutral, 'inaetive, or non-"delivering position, it is clear that-it would not affect the results described above; actually, should the supply pump fail to deliver,'the eng1ne, hence the pumps themselves, wcuid cease'to run.

Were it possible to maintain the 'n'ozzle 'andits chamber '6 always horizontal, and :to subject a pool of fuel which may rest therein 'only to gravitational force, it is evident that the fuel upon entering would collect until it rises to the level of the spill-'orifiee 8, but would then dlow over the same, acting as avv'ein-and would thereafter flow back along the return line '(since the latter has ample capacity to receive it "if only the circulating pump is assumed to be delivering), and would never rise to alevel to-fiow out of the nozzles discharge "orifice-a. But, 'if the return line l2 be overloaded'be yond *itscapacity, as by inlet thereto beyond'the nozzle, or if 'additional fuel be supplied 'to the s'upplyaline byway of the supply pump l'3-'eitherisuchzpossibility being within the contemplation rof this inventionthe fuel spilling over the at 8 could not escape as fast as it -enters the chamber 6. wherefore it would rise, until eventually it discharges at the orifice 8, untilmiti'al conditions are restored.

But it is not possible to maintain the nozzle and its chamberjfi 'alwayshorizo'ntal, and always subject only to gravitational 'force. The-nozzles attitude or orientation with relation to the horiduced tubeis'freed of the gravitational and centrifugal forces acting upon the aircraft as a whole, so that it maintains'its attitude and-orientation with respect to the nozzle, the spill orifice 9, and the nozzles discharge orifice 8, while at the same time acting in all other respects as did the theoretical pool discussed above.

So long as the capacity of the return line 12 is not exceeded, fuel will spill out at 9 before it can rise to discharge at '8. So long as the return line I2 can not accommodate the fuel spilling out'at 9, it will accumulate in the chamber 6. until it risessufiiciently to discharge at 8. By so regulating the amount of fuel permitted to accumulate in the chamber 6, the amount thereof discharged at 8 is subject to control to a very fine degree.

The circulating pump 10 is so rated in relation to the design of the burners I and to the supply and return lines II and I2 that in operation it maintains around the circuit a suflicient rate of flow to maintain the circuit and the swirl chambers of all the burners substantially full without of itself causing any fuel to issue through the nozzles discharge orifices 8. That is to say the circulating pump will maintain tubes of fuel within the swirl chambers of all nozzles of thickness consistent with no discharge through the discharge orifices, as illustrated purely diagrammatically in Figure 2. In this condition any fuel injected into the circulating fiow by the supply pump 13 will result in corresponding discharges from the nozzles, and the rate of swirl within the nozzles will ensure effectual atomization of the discharged fuel however small the quantities discharged may be. This is of very great importance when the system forms part of an aircraft continuous combustion turbine engine, owing to the fact that the aircraft will have to operate over a wide altitude range with consequential variations in the engine fuel requirements for the same R. P. M. of the engine.

In Figure 3 there is illustrated a modification of the variable delivery supply pump 13 of Figure l. The pump 13 in this case isreplaced by a variable delivery unit comprising a pump 21 of the fixed displacement type and an associated by-pass 28 extending between the inlet and outlet of the pump. The quantity of fuel permitted to flow along the by-pass 28 is controlled by a relief valve 29 which in turn may be controlled by the setting of a spring 30 on a valve 3 I. The relief valve 29 is a well known expedient for maintaining a constant or maximum pressure in a fluid fiow line.

A further example of spill burners of this general type is disclosed in Peabody British Patent No. 380,117, of September 9, 1932, and an example of the same general type of fuel supply system, incorporating spill burners, is'disclosed in Rover British Patent No. 608,576, of August 8, 1942, accepted September 17, 1948. The Rover system is designed for terrestrial use, where atmospheric pressure differences are negligible,

the type of' speed control; disclosed. therein :ren-

' dersthe systemill-suited for use inaircraft, at

' direct throttle control.

altitudes varying widely, and particularly at extreme upper altitudes where continuous combustion turbine engines, with which the present invention is concerned, are most effective, but require delicate controls.- a I It will be'appreciated that various modifications may be made without-departing from the invention, for example spillbur-ners of different constructions as already alluded to may be'used; other types of pump may be employed; and also the supply pump, as in the Rover patent, Figure 2, may inject-into the-circulating flow in the supplyline-betweenthe circulating pump and the nozzles instead of into the-return line from the nozzles to the circulating pump as shown in the drawings. Also the systemmay beamplified to include various refinements such as speed governors (see Serial No. 62,636, filed November 30, 1948, now Patent No. 2,559,938, issued July 10, 1951), altitude controls (Serial No. 766,003, filed August 4, 1947), and other forms of direct or in- Again, the system may include means whereby the system may be modified so that the pumps serve other functions during starting (Serial No.-36,011, filedJune 30, 1948) or stopping (Serial No. 2,341, filed January 14, 1948, now Patent-No.-2,530,649, issued November 21, 1950) conditions'of the system or in emergencies (Serial No. 2,342, filed January 14,1948). w

Iclaim r 14A liquid-fuel supplysystem especially for aircraft engines, fo'r'supplying fuel to atomizing burner nozzles of thespill-type,which system comprises supply and-return-conduits defining a closed circuit freely open and adapted to be connected to said burner nozzles for delivery of fuel thereto and return of fuel therefrom, a circulating pump of-the fixed stroke type adapted to be driven from the aircraft engine, included in said circuit and of such capacity relative to the supply and return conduits, respectively, as to maintainthe circuit and the burner nozzles substantially full to the, point of overflowing without itself causing any; discharge therefrom, a supply pump of the variable delivery type also adapted to be driven from the aircraft engine, located externally of said circuit, a delivery con duit leading from said supply pump and connectedfor delivery thence intofsaidclo'sed circuit, and throttle'means operatively'connected to said supply pump to vary the effective delivery of fuel by way of said delivery conduit from zero to a maximum, to inject into the closed circuit a controllable excess flow of fuel to effect discharge from the burner nozzles at a rate corresponding to the rate of excess flow so injected by the supply pump.

2. A liquid-fuel supply system especially for an aircraft continuous combustion turbine engine, for supplying fuel to atomizing burner nozzles of the spill type, which system comprises supply and return conduits defining a closed circuit freely open and adapted to be connected to said burner nozzles for delivery of fuel thereto and return of fuel therefrom, a circulating pump of the fixed-stroke type adapted to be driven from the engine, and included in said closed circuit and of such capacity relative to the supply and return conduits, respectively, as to maintain the circuit and the burner nozzles substantially full to the point of overflowing without itself effecting discharge from the burner nozzles, a supply pump of'the variable-delivery type also adapted to be driven from the engine, and located externally 'of said closed circuit, a delivery conduit leading fromzsaid supply pump and connected into said return conduit of the closed circuit for delivery of fuel into the latter, and of a capacity so to deliver -at a rate such that, when added as excess to the fuel circulating in but not discharging from the closed circuit it will effect discharge at the burner nozzles, to maintain a maximum enginespeed, and amanually operable throttle means interposed in said deliveryconduit, and-variable to regulate the rate of fuel supply from the supply pump to theclosed circuit, and hence to the burner nozzles.

3. A liquid-fuel supply system as in claim 2, including automatic pressure-sensitive control means cperativelyconnected to the delivery conduit in advance of the throttle means, and to the supply pump to vary the delivery therefrom, said control means being arranged for automatic operation under the influenced the changes in pressure in said delivery conduit to vary the effective delivery of the supply pump correspondingly, to maintain its output pressure constant.

4. A liquid-fuel supply system as in claim 2, wherein the variable-delivery supply pump is of the variable displacement type and automatic pressure-sensitive control means operatively connected to the delivery conduit in advance of the throttle means, and to the supply pump to vary said supply pumps displacement, said control means being arranged for automatic operation under th influence of changes in pressure in the delivery conduit to vary the efiective delivery of the supply pump correspondingly, and thereby to maintain its outputpressure constant.

5. A liquid-fuel supply system as in claim 2. wherein the system includes additionally controllable pressure-sensitive 'by-pass means operatively connected to the delivery conduit, to be subject to the output pressure of the-supply pump as aifected byvarying the setting of the throttle means, and also connected to the input side of the supply pump, and automatically Loperable by variations in pressure in the delivery conduit to by-pass a portion of the delivered fuel to the input side of said supply pump and thereby to maintain the output pressure constant at the 50 throttle means.

-6. A liquid-fuelsupply'system for an engine of the continuouscombustion turbine type for aircraft propulsion, and hence subject to variations inair-fuel ratio with change of altitude, and including spill-type burner nozzles, said system comprising closed conduit means adapted to be connected to the burner nozzles for supply of fuel thereto and its return therefrom, a circulating pump of the fixed-stroke type adapted to be driven from the engine, and connected -in said closed conduit means, normally operative to circulate fuel therethrough at a rate which corresponds to the engine-s speed, and of a capacity, relative to said closed conduit means, less than suflicient to effect, by itself, at any altitude or engine speed, discharge of fuel at the burner nozzles, a supply pump of the variable-delivery type adapted to be driven from the engine, and located externally of but connected for discharge intosaid closed conduit'means, to supplement the fuel circulating therein at a rate of flow which, at any given altitude, would correspond to the discharge at the burner nozzle and hence to the engines speed, means operatively connected to saidsupply pump for automatic control thereof, and to the delivery therefrom, and sensitive to variations in the delivery pressure, to regulate the actual delivery from said supply pump to maintain its delivery pressure substantially constant at a given altitude, regardless of changes in engine speed, and means operable under control to regulate the amount of fuel discharged into said closed conduit from the supply .pump, andhence the engine speed at all altitudes.

FREDERICK HENRY CAREY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

